2008 Mini Cooper S r56
I could clear the code and car would drive normal for a short time (15 minutes) and almost always, at extended idle, the code would come back. Zero turbo boost. No misfires though. Ten minutes of driving it would clear itself and the turbo was back. My ebay smoke test showed nothing. Stunk up the garage quit well though.

I did two things at the same time during the fix, I believe the actual fix was the valve cleaning.
1. Harbor Freight DIY Walnut Blast.
2. Replaced Throttle Body Housing

Before and after cleaning pictures. Same cylinder. Notice the blue tape pattern on the right side is identical. On the red arrow, it seems as though the carbon buildup was stuck to the runner wall, and when the valve would open, the carbon build-up nearly sealed the air flow runner sides all the way to the valve stem. Almost like a new little deposit based valve-stem guide formed, and that was all the space available for the air to flow past the valve. Highly restricted. Thus, at a given and steady idle of 900 RPM, the engine wasn't pulling the volume of air through the Mass Air Meter that it expected, throwing a "not plausible" air meter volume code.







Just some notes:
The DIY Harbor Freight Blasting was super cheap. I bought the hopper and 25 pounds of walnut media and the nozzle extension to modify the gun. I had a 1.5 hp compressor and shop vac. All the disassembly and intake removal and prep was simple except for the 10 mm rear knee bolt holding the intake was difficult to access, but doable. Modifying the gun was tricky and you need to understand the venturie valve before you ruin it like I did and had to buy a second one.

Someone did a wonderful write up of how to do it. I followed it pretty much, but I bought the Intake vacuum adaptor $80. However, it took me a long time on each cylinder, easily 45 minutes. The gun clogged quite often, half the time I didn't use the vacuum and walnut were everywhere. Later I turned on the air conditioner and 3 pounds of walnut shells blasted my passengers eyeballs (kidding). It was frustrating to say the least. I'm file attaching the writeup. Thanks to the author. Please look for it.

Throttle Body replacement and ECU reset.
- I couldn't see anything wrong with the throttle body but replaced it anyway. I did not have to do any resetting of the ECU with the throttle body like some posts may suggest for different models, just installed the new one. I did, however, disconnect the battery so it would reset as much as possible that way, if at all.
- The car was very, very hard to start the first time. I would crank then wait a few minutes, repeatedly. I finally had to give it gas (accelerator pedal) while cranking, and it showed signs of life but still took repeated attempts. Once it stared and ran for a few minutes. It was back to easy starts.

No more Air Flow code and full power.

I apologize if this is a repetitive post but I want to put the "fix" in the thread title so it will be easier to search and hopefully help someone.

 

Excellent write up. If your cover is still allowing that much oil out there is definitely something wrong with it. There is an oil drain back valve inside the cover. With heat and age it gets hard and isnt very flexible. This valve may be holding oil in the channel, inside the cover, that feeds the pcv port to the turbo. In other words instead of draining back into the engine the channel is flooding with oil and flowing to the pcv port.
good work on the intake cleaning.